Ceph » CephFS

 8614 2021-12-16T10:02:42.596+0800 14c148b75700  5 mds.0.log _submit_thread 2829812324~1725281 : ESubtreeMap 1653 subtrees , 1651 ambiguous [metablob 0x1, 1973 dirs]
 8615 2021-12-16T10:02:42.597+0800 14c148b75700  5 mds.0.log _submit_thread 2831537625~520 : EImportStart 0x2000000000f from mds.1 [metablob 0x2000000000f, 1 dirs]
 8616 2021-12-16T10:02:42.624+0800 14c148b75700  5 mds.0.log _submit_thread 2831538165~1724401 : ESubtreeMap 1652 subtrees , 1650 ambiguous [metablob 0x1, 1972 dirs]

The `ESubtreeMap` event will be inserted to each new LogSegment when starting a new one. The above logs was reproduced by creating 2000 diretories by using:

# ceph fs set a max_mds 2
# mkdir lxb; setfattr -n ceph.dir.pin -v 1 lxb
# for i in {0..2000}; do mkdir lxb/dir2_$i; setfattr -n ceph.dir.pin -v 1 lxb/dir2_$i; done
# ceph fs set a max_mds 1

If I create more directories the size of the `ESubtreeMap` event will reach up to more than 4MB, that means each LogSegment will only contain the `ESubtreeMap` event:

256350 2021-12-16T09:56:39.804+0800 14c14a582700 10 mds.0.log submit_entry also starting new segment: last = 2055/18446744073709551615, event seq = 2056                                                                                                                                           
256351 2021-12-16T09:56:39.804+0800 14c14a582700  7 mds.0.log _prepare_new_segment seq 2057
...
256500 2021-12-16T09:56:39.810+0800 14c14a582700 10 mds.0.log submit_entry also starting new segment: last = 2057/18446744073709551615, event seq = 2058                                                                                                                                           
256501 2021-12-16T09:56:39.810+0800 14c14a582700  7 mds.0.log _prepare_new_segment seq 2059